Overweight and obesity are important surgical problems. As major contributing factors to the pathogenesis of many disease processes treated by the surgeon, overweight and obesity have a profound impact on present day surgical practice. The broad, long-term objective of our research has been to study the molecular basis of overweight and obesity. Because of the key role of the hypothalamus in the control of body weight we have approached our study of overweight and obesity by examining hypothalamic genes involved in energy homeostasis. In this competing renewal we outline a plan to continue this avenue of research. We propose to continue our study of the hypothalamic melanocortinergic system, an important energy homeostatic system that consists of the melanocortin receptor (MCR) subtypes MC3R and MC4R, the opposing neuropeptides alpha melanocyte-stimulating hormone (alpha-MSH) and agouti-related protein (AgRP), and syndecan-3. We also propose to continue our analysis of hypothalamic gene expression changes that accompany states of energy imbalance. To continue research that was initiated in the original RO1 this proposal has four specific aims. Specific Aim 1 is to identify MC4R ligand binding pockets. This will involve three-dimensional computer modeling of the MC4R and receptor mutagenesis. Specific Aim 2 is to identify the functional regions of AgRP. This will involve the synthesis of modified AgRP proteins. The intent of Specific Aims 1 and 2 is to examine at a molecular level the interactions that occur between components of the melanocortinergic system. Specific Aim 3 is to identify hypothalamic genes that are differentially expressed in the food-deprived rat and the obese Ay mouse, a mouse that has a defect in the melanocortinergic system. This will involve the use of differential gene expression technologies. Specific Aim 4 is to study the role of minoxidil sulfotransferase, serum glucocorticoid-inducible kinase, and EST AA818585, genes identified by our microarray studies, in energy homeostasis. This will involve the use of neuroanatomical techniques and in vivo physiological experiments. The intent of Specific Aims 3 and 4 is to expand understanding of the complex process of energy homeostasis.